Inheritance in Java with Examples

Introduction

Inheritance is a fundamental object-oriented programming (OOP) concept that enables the creation of new classes (subclasses) based on existing ones (parent classes or superclasses). Subclassing allows you to:

• Reuse code: Subclasses inherit fields and methods from their parent class, reducing redundancy and promoting code maintainability.
• Extend functionality: Subclasses can add new fields and methods, tailoring the inherited behavior to specific needs.
• Model real-world relationships: Inheritance mirrors hierarchical relationships between objects, like “Car is a type of Vehicle.”

Key Concepts

• extends keyword: To create a subclass, use extends followed by the parent class name:

Java

class Subclass extends Superclass {
    // ...
}

• IS-A relationship: Inheritance represents an “is-a” relationship between classes. A subclass is a specialized version of its superclass.

Basic Example

Java

class Animal {
    public void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal {
    public void bark() {
        System.out.println("Woof!");
    }
}

• Dog inherits the eat() method from Animal.
• Dog adds its own bark() method.

Accessing Superclass Members

• Use super to access superclass members from a subclass:

Java

class Bird extends Animal {
    public void fly() {
        System.out.println("Flying...");
    }

    public void eat() {
        super.eat(); // Call the superclass eat() method
        System.out.println("Pecking for seeds...");
    }
}

Method Overriding

• Subclasses can override inherited methods to provide specialized behavior:

Java

class Cat extends Animal {
    @Override
    public void eat() {
        System.out.println("Eating cat food...");
    }
}

Types of Inheritance

• Single Inheritance: A subclass inherits from one superclass.
• Multilevel Inheritance: A subclass inherits from a subclass, creating a chain of inheritance.
• Hierarchical Inheritance: Multiple subclasses inherit from a single superclass.
• Multiple Inheritance: A subclass inherits from multiple superclasses (not directly supported in Java, but achievable through interfaces).

When to Use Inheritance

• Code reuse and avoiding redundancy.
• Extending functionality of existing classes.
• Modeling real-world hierarchical relationships.
• Creating class hierarchies for better organization.

Conclusion

Inheritance is a powerful OOP tool for code organization, reusability, and extensibility. Understanding its principles and applications is essential for designing well-structured and maintainable Java applications.